The present invention relates to a method for producing a silicon single crystal wafer which has a defect-free layer (DZ layer, Denuded Zone) in a surface layer part, and has sufficient gettering sites in a bulk part.
It is required for a silicon single crystal in the light of characteristics of a device that a surface layer part which serves as an active layer of device has no crystal defects. Furthermore, there is required a wafer (IG wafer) having a high intrinsic gettering (IG) effect which has gettering sites for heavy metal contamination in a bulk part of the wafer, since there exists in a process for fabricating a device a process wherein heavy metal contamination which degrades device characteristics is easily caused.
As a method for forming oxide precipitates or crystal defects such as dislocations and stacking faults resulting from them (hereinafter referred to as oxygen induced defects) in a wafer, there is known, for example, a method wherein a CZ silicon single crystal wafer which is produced by Czochralski (CZ) method and contains interstitial oxygens at a certain concentration is subjected to a multi-stage IG heat treatment (for example, a three stage heat treatment of high temperature, low temperature and medium temperature, or the like) to form a DZ layer in the surface layer part and form oxygen induced defects in the bulk part.
However, if an IG wafer having high IG ability is produced according to such a method, there is a disadvantage that the oxygen induced defects tend to be increased also in the surface layer part used serving as a device active layer. This is because, the IG ability is greatly dependent on the amount of oxide precipitates (a density of oxide precipitates) in the wafer, and thus there has been employed as the easiest method of improving it, a method in which concentration of interstitial oxygen contained in the silicon wafer to be subjected to IG heat treatment is increased, but at the same time increase of oxide precipitates in a surface layer part of the wafer are also caused. Moreover, in the case that heat treatment is performed for a long time in order to induce crystal defects at a high density inside, oxygen induced defects which exists inside are significantly grown with the prolonged heat treatment, which may reach the device active region in some cases.
Furthermore, as a grown-in defect formed in a CZ wafer during crystal growth according to Czochralski method, it is known that in addition to a minute oxide precipitates, a void type crystal defect (hereinafter referred to as a void defect (referred to also as COP)) which is considered to be an agglomerations of vacancies is existed. And, it is known that the void defects remain in a DZ layer of a conventional IG wafer. That is, even in a DZ layer (a defect-free layer), defects actually eliminated (reduced) are the defects due to oxide precipitates, and such void defects are not reduced.
It has been required that the wafer having an excellent gettering ability wherein no crystal defects exist in a region to a certain depth from a surface and sufficient gettering sites such as a oxide precipitates exist in a region deeper than a certain depth is produced efficiently. The reason for needing the excellent gettering ability is that the influence of a heavy metal impurity is one of the causes of reducing the yield in a device process, and that insufficient formation of gettering sites such as oxide precipitates in a wafer causes shortage of gettering, and thus heavy metal is captured in the device active layer to cause degradation of device characteristics such as increase in a leakage current.
Of course, the best way is to keep cleanliness in all the steps of a device process, but it is actually impossible to prevent a wafer completely from suffering from heavy metal contamination or the like. Therefore, it is desired that the oxygen induced defects serving as gettering sites are formed sufficiently inside a wafer. On the other hand, as for the surface layer part serving as a device active layer, it is desired that the region having neither oxide precipitate nor crystal defect such as a void defect exist to a sufficient depth.
The main object of the present invention is to provide a method for producing a silicon single crystal wafer which has a DZ layer of higher quality compared with a conventional wafer in a wafer surface layer part and has oxygen induced defects at a sufficient density in a bulk part.
In order to achieve the above-mentioned object, a method for producing a silicon single crystal wafer of the present invention is a method for producing a silicon single crystal wafer which contains oxygen induced defects by subjecting a silicon single crystal wafer containing interstitial oxygen to a heat treatment wherein the heat treatment includes at least a step of performing a heat treatment using a resistance-heating type heat treatment furnace and a step of performing a heat treatment using a rapid heating and rapid cooling apparatus.
As described above, according to the present invention, as a precipitation heat treatment for forming gettering sites such as oxide precipitates or the like in a bulk part and a heat treatment for eliminating void defects in the surface of a wafer, there are conducted both a heat treatment using a resistance-heating type heat treatment furnace (it is a so-called batch processing furnace in which a treatment of two or more wafers can be performed at the same time, generally there are a vertical-type furnace and a horizontal-type furnace) and a heat treatment using a rapid heating and rapid cooling apparatus (it is usually a single wafer processing apparatus, and is a so-called RTA (Rapid Thermal Annealing) apparatus in which it is possible to increase and decrease a temperature to the target temperature in several seconds to several tens of seconds, and a lamp heating type apparatus using an infrared lamp is often employed). By combining the heat treatments by these apparatuses, there can be achieved the effect that generation of oxygen induced defects is promoted and the region where the void defects are reduced (hereinafter occasionally referred to as a void-free region) is enlarged.
In that case, it is preferable that the heat treatment using the resistance-heating type heat treatment furnace is performed at 1000 to 1300xc2x0 C. for 10 to 300 minutes, and the heat treatment using the rapid heating and rapid cooling apparatus is performed at 1000 to 1350xc2x0 C. for 1 to 300 seconds.
This is the suitable range of the heat treatment conditions set for both of the apparatuses used for the heat treatment of the present invention. If it is performed at a lower temperature for a shorter period than the aforementioned range, the effects of promoting oxygen induced defects and enlarging the void-free region becomes insufficient. On the contrary, if it is performed at a higher temperature for a longer period, cost may be increased for the reason that degradation of device characteristics due to heavy metal contamination becomes remarkable, a problem arises in a durability of the apparatus due to increase of load on the apparatus, throughput is reduced and the like, and thus it is not practical.
In this case, it is preferable to use as the silicon single crystal wafer to be subjected to the heat treatment, a silicon single crystal wafer which is doped with nitrogen at a concentration in the range of 1xc3x971010 to 5xc3x971015 number/cm3.
If it is doped with nitrogen, although a density of grown-in defects is increased, a size of them becomes small. Therefore, by performing the heat treatment, the grown-in defects in a surface layer part can be eliminated efficiently, and a high density of oxide precipitates can be obtained in a bulk part. If nitrogen concentration is lower than the lower limit, the above-mentioned effect of nitrogen doping can not be fully achieved. If nitrogen concentration is higher than the upper limit, formation of a single crystal is inhibited when the crystal is grown
In addition, it is preferable to use the silicon single crystal wafer which is doped with carbon at a concentration in the range of 0.1 to 5 ppma as the silicon single crystal wafer to be subjected to the heat treatment.
As described above, oxygen precipitation can be promoted also by doping with carbon, and the concentration of 0.1 ppma or more is needed in order to obtain the effect. If it is more than 5 ppma, formation of a single crystal is inhibited when the single crystal is grown as in the case of nitrogen doping.
According to the present invention, there is provided a silicon single crystal wafer having a defect-free layer in which there exist neither oxygen induced defect nor crystal defect such as a void defect in a surface layer part, and having sufficient gettering sites in a bulk part which is produced by the above-mentioned production method.
According to the present invention, there can be produced a silicon single crystal wafer which has a DZ layer of a higher quality than the conventional wafer in a surface layer part of the wafer, contains a sufficient density of oxide precipitates in a bulk part, and has a high gettering ability.